1. Field of the Invention
This invention relates to an ophthalmic apparatus having what is referred to as a "fogging" optical system and a detecting optical system.
2. Description of Related Art
FIG. 6 is a schematic diagram illustrating the structure of a conventional ophthalmic apparatus such as an eye refractive power measurement apparatus.
In the ophthalmic apparatus shown in FIG. 6, visible light from a gazing target 69 passes through a projecting lens 68, a stop 67, a lens 63, and half mirrors 64 and 62. This visible light then reaches an eye 61 to be examined. An image of the gazing target 69 is formed on the retina of the eye 61. The gazing target 69, the projecting lens 68, the stop 67, and the lens 63 together form a fogging optical system for relaxing the eye 61 for proper examination.
The ophthalmic apparatus shown in FIG. 6 has an eye refractive power measurement optical system 71 for measurement of the refractive power of the eye 61 to be examined. Infrared (IR) light for measurement is emitted from the eye refractive power measurement optical system 71 and reflected by a mirror 70 and a half mirror 62. The IR light is projected on the fundus of the eye 61 for examination and then reflected from the fundus of the eye 61. A portion of the IR light goes back along the optical path having the half mirror 62 and the mirror 70 and is incident on a light-receiving element located inside of the eye refractive power measurement optical system 71. The refractive power of the eye 61 is measured based on the photoelectric output of the light-receiving element.
The IR light reflected from the eye 61 is also partially transmitted through the half mirror 62 and reflected by the half mirror 64. The light reflected by the half mirror 64 passes through an image-forming lens system including a lens 72 and a lens 65. This light forms an image of the eye 61 on an image pickup plane 66. In this way, the lens 72, the lens 65, and the image pickup plane 66 together form an image pickup optical system for detecting image information relating to the eye 61 undergoing examination.
When a fogging optical system is used for removing the accommodation power of an eye under examination, the diameter of the human pupil is small and the F-number is relatively large. The field angle is relatively large in order to alleviate instrumental myopia influences. In the image pickup optical system for observing the eye and the ophthalmic measurement optical system for measurement of refractive power information of the eye, however, the F-number is relatively small in order to guarantee the provision of a prescribed light amount. The field angle (or the height of the object) is also relatively small. Optical systems having properties entirely different from each other, therefore, coexist in the ophthalmic measurement and other ophthalmic apparatuses.
When efforts are made to reduce the sizes of ophthalmic apparatuses having these optical systems, reductions in the focal lengths of various lens groups forming each optical system may be used. However, in order to reduce the focal lengths of the various lens groups while ensuring the desired optical characteristics for each optical system, the number of lenses forming each lens group becomes larger. This is a disadvantage.